Since the advent of high temperature water tube boilers which burn fuels having substantial slag content, and also with the adoption of certain high temperature processing-type heat exchangers, the removal of adherent deposits from the fire side surfaces has been an increasingly severe problem. Sootblowers employing jets of steam and/or air cannot remove some such deposits. It has long been known that jets of water can be used to assist in slag removal, and it was also understood for many years that the thermal shock and resultant embrittlement of the slag caused by a water jet, combined with the energy of the jet itself, could often dislodge slag not removable from a steaming boiler by other means. However, until the advent of the so-called constant jet progression system disclosed in U.S. Pat. No. 3,782,336 granted Jan. 1, 1974 to J. E. Nelson, it was frequently impractical to use water jets for this purpose, because it was not possible to control and limit the thermal shock to a value which would avoid premature failure of the tubes. Prior to the advent of the constant jet progression system, very costly damage had been caused by some uses of water under difficult cleaning conditions.
Basically, the present invention aims to improve upon the Nelson constant jet progression water lance-type cleaning systems as currently used by increasing still further, and to a very substantial degree, the ratio between the peak impact pressure exerted by the jet and both the water volume required and the thermal shock imposed on the tubes.
A related object is to provide means for removing such deposits more quickly and economically than has heretofore been feasible without damage to the heat exchanger.
A further object is to increase the overall efficiency of the boiler by substantially reducing the absorption of heat from the gas stream by the cleaning medium.
Other objects and advantages of the invention will become apparent to persons skilled in the art upon consideration of the present disclosure in its entirety.